The present invention relates generally to separation processes and medical treatments. More specifically, the present invention relates to separation membranes and to medical fluid treatments using such membranes, such as treatment of renal failure and fluid removal from persons whose kidneys do not function well.
Hemodialysis in general uses diffusion to remove waste products from a patient's blood. A diffusive gradient that occurs across the semi-permeable dialyzer between the blood and an electrolyte solution called dialysate causes diffusion. Hemofiltration is an alternative renal replacement therapy that relies on a pressure difference and thus a convective transport of toxins from the patient's blood. This therapy is accomplished by adding substitution or replacement fluid to the extracorporeal circuit during treatment (typically ten to ninety liters of such fluid). That substitution fluid and the fluid accumulated by the patient in between treatments is ultrafiltered over the course of the hemofiltration treatment, providing a convective transport mechanism that is particularly beneficial in removing middle and large molecules (in hemodialysis there is a small amount of waste removed along with the fluid gained between dialysis sessions, however, the solute drag from the removal of that ultrafiltrate is not enough to provide convective clearance).
Hemodiafiltration is a treatment technique that combines convective and diffusive clearances. Hemodiafiltration uses dialysate to flow through a dialyzer, similar to standard hemodialysis, providing diffusive clearance. In addition, substitution solution is provided directly to the extracorporeal circuit, providing convective clearance.
Home hemodialysis has declined in the last twenty years because costs have increased, but reimbursement or insurance coverage has not increased, even though the clinical outcomes of this technique are more attractive than conventional hemodialysis. One of the drawbacks of home hemodialysis is the need for a dedicated water treatment, which includes equipment, water connection and drainage. Installing and using those components is a difficult and cumbersome task that can require a patient's home to be modified. Nevertheless, there are benefits to daily hemodialysis treatments versus bi- or tri-weekly visits to a treatment center.
In particular, a patient receiving more frequent treatments removes more toxins and waste products than a patient receiving less frequent but perhaps longer treatments, leading to a healthier, more energetic person. What is needed is a better way to rid a patient's blood of small and even mid-size molecules, a better way that could involve a combination of known and reliable convective and diffusive transport of the small and medium molecules through the dialysis membranes.